Conventionally, a conductive composition constituted from the mixing of a definite amount of a metal powder into a resin, has been widely used in the paste for thick conductor, a conductive adhesive and the like.
As such metal powders used in the conductive composition, for example, a reduced Ag powder made from the reduction reaction from Ag (silver) nitrate by using the reducing agent such as hydrazine, formaldehyde, and ascorbic acid are known and disclosed in JP H8-92611A and the like. Also, in JP H10-183208A and the like, a fine non-aggregated Ag powder and a flake type Ag powder made from pyrolysis are disclosed. Also, in JP H7-109501A and the like, a fine non-aggregated Ag powder and a flake type Ag powder made from grinding procedure are disclosed. Moreover, in JP H9-125110A, a dendrite Ag powder made from electrolysis is disclosed.
However, since every conventional metal powders is aiming to conduct via point contacting of the surfaces of the adjoining metal powders, there has been the drawbacks that the contact area is small and the conductive resistance between the conductive substrates in condition that a resin is included, is high.
Further, the conventional metal powders generally show the low conductivity in condition that a resin is included, and many metal powders are required into the resin to obtain the fixed conductive resistance between the conductive substrates. Therefore, there were the drawbacks that the viscosity of the conventional conductive composition becomes high and the handling-ability becomes worse. To improve the handling-ability, the additional quantity is restricted to be the low level and much diluent such as organic solvents are required.
Thus, the mixing usage of spherical Ag powder and Ag flake powder has been proposed. However, as shown in the comparative example 1 of table 2, the electrical resistivity for the conductive composition obtained from mixing the plural conductive powders was about 1.4×10−3Ω·cm which was insufficient. On the other hand, the conventional metal powders have the broader particle size distribution, which may cause the short-circuit problem or insufficient mixing problem into the resin.
In view of the above drawbacks, inventors of the present invention have keenly studied and found that a conductive powder which can show the highly conductivity (low resistivity) even in condition that a resin is included, and the narrow particle size distribution, can be obtained by including the core material to strengthen the crystal growth reaction and forming the convex radially extended and a concave among the convex.
Accordingly, it is an object of the present invention to provide a conductive powder which can show the highly conductivity (low resistivity) even in condition that a resin is included and can has the narrow particle size distribution, and a conductive composition using the same, and a producing method of the same.